Reduction of Escherichia coli O157 : H7 counts on whole fresh apples by treatment with sanitizers

The objectives of this study were to determine if washing of whole apples w ith solutions of three different sanitizers (peroxyacetic acid, chlorine di oxide, or a chlorine-phosphate buffer solution) could reduce a contaminatin g nonpathogenic Escherichia coli O157:H7 population by 5 logs and at what s anitizer concentration and wash time such a reduction could be achieved. Sa nitizers were tested at 1, 2, 4, 8, and 16 times the manufacturer's recomme nded concentration at wash times of 5, 10, and 15 min. Whole, sound Braebur n apples were inoculated with approximately 1 x 10(8) or 7 x 10(6) CFU per apple, stored for 24 h, then washed with sterile water (control) or with sa nitizers for the prescribed time. Recovered bacteria were enumerated on try pticase soy agar. Washing with water alone reduced the recoverable populati on by almost 2 logs from the starting population; this can be attributed to physical removal of organisms from the apple surface. No sanitizer, when u sed at the recommended concentration, reduced the recovered E. coli populat ion by 5 logs under the test conditions. The most effective sanitizer, pero xyacetic acid, achieved a 5-log reduction when used at 2.1 to 14 times its recommended concentration, depending on the length of the wash time. The ch lorine-phosphate buffer solution reduced the population by 5 logs when used at 3 to 15 times its recommended concentration, depending on wash time. At no concentration or wash time tested did chlorine dioxide achieve the 5-lo g reduction.